WO 2004/080492 discloses a method of radiofluorination of a vector which comprises reaction of a compound of formula (I) with a compound of formula (II):
or a compound of formula (III) with a compound of formula (IV)
wherein:                R1 is an aldehyde moiety, a ketone moiety, a protected aldehyde such as an acetal, a protected ketone, such as a ketal, or a functionality, such as diol or N-terminal serine residue, which can be rapidly and efficiently oxidised to an aldehyde or ketone using an oxidising agent;        R2 is a group selected from primary amine, secondary amine, hydroxylamine, hydrazine, hydrazide, aminoxy, phenylhydrazine, semicarbazide, and thiosemicarbazide and is preferably a hydrazine, hydrazide or aminoxy group;        R3 is a group selected from primary amine, secondary amine, hydroxylamine, hydrazine, hydrazide, aminoxy, phenylhydrazine, semicarbazide, or thiosemicarbazide, and is preferably a hydrazine, hydrazide or aminoxy group;        R4 is an aldehyde moiety, a ketone moiety, a protected aldehyde such as an acetal, a protected ketone, such as a ketal, or a functionality, such as diol or N-terminal serine residue, which can be rapidly and efficiently oxidised to an aldehyde or ketone using an oxidising agent;to give a conjugate of formula (V) or (VI) respectively:        
                wherein X is —CO—NH—, —NH—, —O—, —NHCONH—, or —NHCSNH—, and is preferably —CO—NH—, —NH— or —O—; Y is H, alkyl or aryl substituents; andthe Linker group in the formulae (II), (IV), (V) and (VI) is selected from:        
wherein n is an integer of 0 to 20; m is an integer of 1 to 10; p is an integer of 0 or 1; Z is O or S.
WO 2006/030291 discloses a method for radiofluorination comprising reaction of a compound of formula (I):
wherein the vector comprises the fragment:
with a compound of formula (II):
wherein:n is an integer of 0 to 20;m is an integer of 0 to 10;Y is hydrogen, C1-6alkyl, or phenylto give a compound of formula (III):
wherein m, n, and Y are defined as for the compound of formula (II) and the vector is as defined for the compound of formula (I).
Glaser et al [Bioconj. Chem., 19(4), 951-957 (2008)], describe the synthesis of 18F-labelled aldehydes, including 18F-fluorobenzaldehyde, and their conjugation to amino-oxy functionalised cyclic RGD peptides.
Speranza et al [Appl. Rad. Isotop., 67, 1664-1669 (2009)] describe an automated synthesis of [18F]-fluorobenzaldehyde ([18F]-FBA) using a TRACERlab™ apparatus. A hand-made purification device is used to purify the [18F]-FBA. Speranza et al describe the fact that cartridge purification is preferred over HPLC purification for automated synthesizer apparatus syntheses. Their cartridge methodology, however, suggests that dichloromethane or chloroform are the best solvents for [18F]-FBA purification. Both solvents have unsuitable toxicological properties for in vivo use, and are immiscible with water. The method is therefore unsuitable for radiopharmaceutical preparations.
Battle et al [J. Nucl. Med., 52(3), 424-430 (2011)] disclose monitoring anti-angiogenic therapy with [18F]-fluciclatide:

Battle et al mention that the [18F]-FBA used was purified by diluting with water, and trapping on a solid-phase extraction (SPE) cartridge. Impurities such as precursor, DMSO, Kryptofix-222 and hydrophilic by-products were said to be eluted to waste, and the [18F]-FBA subsequently eluted with ethanol. The present inventors have, however, found that using a C18 SPE cartridge only some of the precursor is eluted to waste, and the remainder co-elutes when the [18F]-FBA is eluted with ethanol.
There is therefore still a need for alternative methods of labelling biological targeting moieties with 18F.